Circuit interrupters



Jan. 19, 1960 c. F. CROMER ET AL CIRCUIT INTERRUPTERS Filed Dec. 20, 1956 6 Sheets-Sheet 1 2%: 1 .9 m% h IO I -4 l I u.

INVENTORS Charles F. Cromer 8- Benjamin R Baker ATTORNEY Jan. 19, 1960 c. F. CROMER ET AL 2,922,010

CIRCUIT INTERRUPTERS Filed Dec 20, 1956 6 Sheets-Sheet 2 Jan. 19, 1960 c. F. CROMER ET AL CIRCUIT INTERRUPTERS 6 Sheets-Sheet '4 Filed Dec. 20, 1956 Oil Level Air Filled With US Oil Fig.6.

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Jan. 19, 1960 c. F. CROMER ETAL CIRCUIT INTERRUPTERS 6 Sheets-Sheet 5 Filed Dec. 20, 1956 United States Patent 2,922,010 I CIRCUIT .INTERRUPTERS -Charles F. Cromer, Trattord, 'and Benjamin P. 'iBaker, Monroeville, Pa assignors sto Westinghouse Electric Corporation, E'East z-Pittsburgh, Pa., :a corporation of Pennsylvania ApplicationDecemher 20,1956, Serial No."629,636

.7 Claims. (0]. 200-148) This invention relates to circuit interrupters in general and, .more particularly, to .arceextinguishing :structures therefor.

A general object of-the presentainvention .is to provide an improved circuit interrupter in which are elongation and are extinctionare .very rapidly achieved,to.result in more efficient circuit interruption than has been achieved inv circuit interrupters heretofore used.

-A more specific object of thepresentinvention isto provide an improvedfluid+blast circuit interrupter utilizing a piston construction, in which fluid ismore quickly compressed within the piston assembly :to :morequickly eifect arc-extinction, :an'dyetmeans are provided to insure an adequate isolating gap in the open-circuit position.

Yet, afurther object of "the invention isto provide 'an improvedflui'd-blast circuit interrupter in which a:mov- :able cylinder assembly carrying the movable contact moves over a relatively'stationary piston to inject :fluid into the established :arc, and wherein the relatively stationaryzpiston is subsequentlymovable with ,the movable 1 :cylinder assembly to result inan isolating gap distance of sufficient length in :the open-circuit positioncf the :inter rupter.

In the United States patent application filed December 20, 1956, Serial No.-629,6'04, now United States Patent No. 2,866,045, issued December 23, 1958, to Winthrop M. Leeds, and :assignedto the assignee'of the instantapplication, there -is-shown and described a circuit interrupter of the single-bushing type, in which the grounded intermediate part of the terminal bushing is supported by a grounded framework, and wherein an interrupting unit is secured to the interior end of the terminal bushing, being surrounded thereabout by an insulating casing. Suitable means operating from the grounded intermediate support :for the terminal bushing is .e'ifective to :operate an operating :cylinder over a piston :arrangement, which was stationary in the aforesaid application.

It is -'a further :object :of the present invention :to imzprove upon the single-bushing type of circuit :interrupter set out in the foregoing Leeds application, in'which fluid pressure .is more quickly brought about, and-yet an adequate isolating-gap is obtained when thecircuitainterrupter is moved to the open-circuit position.

Further objects .and advantages will readily Ebecome apparent -:upon reading'the following specification, taken :inrconjunction with the drawings, in which:

Fig. 1 is a side elevational'viewof a single-bushing 'type of circuit interrupter embodying the :present invention, and:shown in the closed-circuit position;

Figs. 2A and 2B collectively illustrate an enlarged, 'sectional view taken through the circuit interrupter of .Fig. 1, with a portion :of the terminal bushing omitted, and :the .contact structure being illustrated in the closed-circuit position;

Fig. 3 is :a fragmentary sectional view similar to that of Fig. 2B, but illustrating the position of 'the several parts imthe fullytopenecircuitposition;

-.tical:sectionaliview'through a modified type of interrupt- .ingzassembly, the contact structure :beingxshown in the 'closedmircuit position; and

Fig. 6 is a'longitudinal, sectional view takenithrough .the shock absorber utilized in the interrupter of 'Fig. 5B.

:Referring ito the :drawings :and :more :particularly to :Fig. ;1 thereof, the reference numeral 51 generally desig- 'nates .a circuit :interrupter :of the single-bushing :type. The circuit interrupter 1 generally includes :a terminal bushing, generally .designated byJthe'Ieference numeral 12, which :maybe .of substantiallystandard construction having .a :current transformer 2A 'thereabout.

The intermediate, grounded, central portion .of the terminal bushing .2 isclampedto, and supported by, an intermediate grounded mechanism housing 3, which is supported by:a grounded framework :4, composedof vertically ex- ..tending angle-iron members :5 and cross-braces -6, also of:angle+iron construction, which may be welded thereto.

As illustrated in Fig. 1, a mechanism "housing comwhich form no part-of'the present'invention. The-operating mechanism Within the compartment '3A 'may be .employed to etfectvertical'reciprocal'motion 'ofa link 7 having a bifurcated upper end, which is pivotally con- ;nected, as-at 8, :to an arm 9, the latter being fixedly secured to a horizontally extending operating shaft "10. The operating shaft 10 may be journaled within a pair of brackets 11, the latter being supported 'by the cross- '14, the-latter being fixedly connected -to a vertically ex- 40 tendingoperating shaft'IS. Alsosecured'to the operat- -thereto, is a spring :arm '16 pivotally connected, as at ing shaft 15, and extending outwardly at right angles 17, to a spring .rod 18. The spring rod 18'extends interiorly within a spring housing 19, 'the latter housing a coiled compression spring, not shown, which seats .=against one-end 20 of the spring housing 19, 'and'has its :other end seated upon a washer fixedto the outer end off-the spring rod 18, and forming a spring seat. The

accelerating compression spring disposed within the subular spring housing 19 to move the spring rod 18 to the right, acting upon the spring arm '16 and effecting rotative opening motion of the operating shaft 15.

Although Fig. 1 illustrates the interrupter 1 in a horizontalposition, it can be mounted in any position such as the vertical position, and Figs. 2A and 2B show this slight variation. Referring more particularly to Figs. 2A "and 2B, which illustrate a longitudinal sectional view through a portion of the circuit interrupter'lmounted in a vertical position, it will be observed that the mechanism housing 3 has affixed thereto a clamping sleeve 22, to which is secured, as by a number of bolts 23, the terminal bushing 2. A clamp '24 encircles the rotatable operating -shaft15,'being.clamped thereto by a bolt 25. The clamp '24 has secured thereto a yoke member 26 '(Fig. 5A).

The outer ends 27 of the yoke member 26 are pivotally connected by pins 28 to a pair of insulating operating 3 nated by the reference numeral 30, and including an operating cylinder 31. In. other words, the lower ends of the two insulating operating rods 29 are pivotally connected to the side walls of the movable operating cylinder 31.

The operating cylinder 31 has a spider plate 32 secured to the lower end thereof by any suitable means, to which is clamped, by bolts 33, a clamping flange 34, the latter serving to clamp an insulating orifice. member 35 to the spider plate 32. The orifice member 35 has an orifice opening 36, through which extends, inthe closed-circuit position, a relatively stationary contact 37. The relatively stationary contact 37 makes abutting contacting.

engagement with a movable contact 38,'the latter being fixed to the spider plate 32 and having an upwardly extending contact extension 39. The contact extension 39 makes sliding contacting engagement with a plurality of laterally flexible contact fingers 40 integrally formed with a contact foot 41, the latter being threadedly secured to the lower threaded end of a terminal stud 42 a ring-shaped plate 47 secured thereto with a central I opening 48, through which slides the contact extensio 39 during the opening and closing operations.

A relatively stationary piston 49 has secured thereto a plurality of piston rods 50,.the upper endsvof which are operatively associated with a plurality of shock-ab sorber assemblies 51, the internal construction of which is more readily apparent from an inspection of-Fig. 4

of thedrawings,

Generally, the shock-absorber assemblies 51, shown in Fig. 4, include a piston 52 secured to the upper end of the piston rod 50 and having a pivotally mounted flap valve 53 controlling a passage 54 through the upper end of the piston rod 50. The piston rod 50 is biased downwardly by a compression spring 55, the upper end of which seats against the lower end 56 of a container 57 containing a suitable amount of shock-absorber fluid, such as oil, to the level 58. A plug 59, disposed at the upper end of the container 57, may be used for replenishing the oil 60.

The piston 52 has a plurality of restricted passages 61 therethrough, through which the oil may leak relatively slowly. The piston 52 moves within a piston cylinder 62, the latter having openings 63 and 64, and dis- 7 posed within a closed outer cylinder 65. The lower end of the cylinder 62 has an outwardly extending flange-66, which 1s clamped, by a flange ring 67, to the plate 47 by means of bolts 68. Preferably, a gasketed seal 69 prevents any interexchange of fluid lengthwise along the p1ston rod 50.

Referring back to Fig. 2B, it will be noted that the relatively stationary contact 37 has a lower portion 70 which bears against a plurality of flexible contact fingers 71, the latter being integrally formed with an apertured plug 72 inserted within a stationary contact housing 73. The contact housing 73 may be suitably clamped to a lower closure plate 74. The closure plate 74 is suitably secured by means, not shown, to a flange ring 75 secured by cement 76 to a casing 77, the latter being preferably formed from a suitable weatherproof material, such as porcelain.

In the closed-circuit position of the interrupter 1, as illustrated in Figs. 1, 2A, 2B and Fig. 4, the electrical circuit therethrough includes the terminal stud 42 (Fig. 1), through the terminal bushing 2 to the contact foot 41. The circuit then extends by way of the flexible fingers 40 to the contact extension 39, through the movable contact 38 and through the relatively stationary conthe mechanism disposed withinfthe mechanism compartment 3A. This unlatching will permit the accelerating compression, spring, disposed in spring housing 19, to effect, through the spring rod 18, rotative motionof the spring arm 16 and hence clockwise rotativemotion of the operating shaft 15, as viewed in Fig. 2A.

5 The rotation of the operating shaft 15 will eifect, through the yoke 27 and insulating operating rods 29, upward opening movement of the movable operating cylinder assembly 30. This will cause upward movement of the movable contact 38, the relatively stationary contact 37 following this opening motion for a predetermined time, until a shoulder 79, formed on'the plug '78, strikes the surface 80 on the plug 72. When this occurs, the movable contact 38 will separate'upwardly away from the stationary contact 37 drawing an are 81, shown in Fig. 3, for clarity, even though Fig. 3 illustrates the fully open-circuit'position of the interrupter.

It will be observed that the upward movement of the operating cylinder 31 over the piston 49 will diminish the volume within the region 82 (Fig. 2B), thereby compressing the fluid, such as SF therein, forcing the latter downwardly through apertures 83 within spider plate 32 and through the orifice opening 36 to effect extinction of the are 81.

It is desirable to provide such a flow of gas through the' on'fice 36 by the compression of the volume of gas confined in the region'82 of the operating cylinder 31. The differential pressure P which can-be produced across theinterrupting orifice 35 is a function of the initial absolute pressure P; and the ratio of the initial volume V to the second, or reduced volume V Let it be assumed that in order to interrupt a fixed current, a required pressure differential, P is necessaryand v or the differential pressure is a function of the ratios of the initial and final lengths (L and L of the cylindrical volume. Then if the initial length is reduced, the required pressure differential can be obtained with a shorter travel, and result in a proportionate reduction of arcing time'or dead-time.

Although interruptions can be obtained at this reduced gap length, in order to meet required voltage test specifications, a longer isolation gap is required.

This invention proposes a method in which the shorter 1 interrupting times may be obtained, and further provides for the necessaryisolating gap, and in so doing eliminates external shock absorbers.

The piston 49 is initially stationary, butthe characteristics of the shock absorber assembly 51 are such that during low-load conditions the piston 49 will not move until the surface 84 of the spider plate 32 strikes it and carries it. with the operating cylinder 31 to the fully open-circuit position, shown in Fig; 3, and providing a greater isolating gap distance between the contacts 37, 38 than would be the case'if the piston 49 werestationary at all times. I I

During the high-fault current conditions, when the. arcwet-922m ring-pressure is I very rapidly built .-up. through jthe-torifice .36

by ;the;arc'8-1, the pressure within region -82 of .theopcrating cylinder 31 will :be :sufficient to =causeslight re- ;traction of the piston 49 even before the surface 84 of the piston 49 must be 1500 pounds before the latter begins to move. It will move-oneinchunder this force,

and then will move oli ering little opposition for the remainingtwo inches of its travel. The surface84 of spider member 32 will be in contact with the piston 19 during the final two inches of travelof piston 49.

To understand the hesitating :action of the relatively fixed piston49, reference maybehad to Fig. 4, wherein ,it will be observed that initially .upward opening travel of the piston rod 50 will be opposed by the suction created in the region 85 under the piston 52. However, ,oil will leak through the restrictedopenings161, until the lower edge 86 of the piston 52 moves above the lower edge 87 of the opening 64, atwhich time there will be unimpeded upward movement of the piston rod150 be- .cause of the circulation of oil around the bypassing subsequently permits relatively free retraction of said ,piston wtih the movable operating cylinder 31 to the fully open-circuit position of Fig. 3.

During the closing operation, the mechanism within the mechanism compartment 3A is actuated to effect downward movement of link 7, thereby effecting simultaneous closing rotation oi: the operating shaft and. charging, or compression, of the accelerating spring disposed within the spring casing 19. This will cause, through the op .erating rods 29, downward closing movement of the opcrating cylinder 31 to effect contact reengagement between contacts 37, 38. A compression spring=88 within .the contacthousing 73, provides the requisite contact pressure. The piston 49 moves quickly downwardly -because of the flap-valve action 53, permitting oil to move quickly out of the chamber 85, below the piston 52 and through the passages 54. This closing motion of the piston rod 50 is not only assisted by the compression spring 55, but it is also assisted by a pluralityof closing springs 89 encircling the piston rods 50, as shown in Fig. 2B.

From the foregoing description, it will be apparent that the use of a hesitating piston 49, which is initially substantially stationary during the initial opening movement, and subsequently movable within the operating cylinder 31, affords a greater isolating gap distance between the contacts 37, 38, and results in a circuit interrupter of very high speed in action, and very quickly causing a considerable pressure differential P across the orifice opening 36 by the relatively short distance L between thespider-plate 32 and the piston 49 which maybe employed. As mentioned hereinbefore, the shorter the distance L is, the less opening travel is required of operating cylinder 31 to build up the requisite differential 6 :sembly 933. The upper tendof .the shock absorber 93 has an apertured lug portion 94, which isfixedly secured to a spiderplate95 bolted.to-.a contactfoot 96 ,bybolts .97.

The-contact -foot 9.6.is ,threadedly secured andclarnped,

.as:by a clampingbolt 9.8,tothe1lower threaded end of .a terminal stud 9')havingta lowerlriecess 100. Extending downwardly from the spider plate 95 .are four contact guide rails ,101, -having,.r e ducedcnds, vwhichare threaded toaccommodate nuts 102. .The spider plate 95 has four apertures toaccommodate the ,reduce,d ends of the contact guide rails 101. The Zlower ends of the contact guide rails 101 are braced iby cross-braces 103, having apertured ends, through which pass the reduced lower end portions 105 of the guide rails 101. Nuts 104, threaded on the vlower ends 105 of the guide rails 101, fixedly secure the apertured cross-braces 10,3inposition.

Bolted to the side walls -.of a movable operating cyl .inder 106 by bolts -107 ,,is ,a movable contact rail 108. vInterposed between the contact rail 108, which is movable with operatingcylinder 106, and thestationary contact rails 101 is a pluralit ycf contact roller assemblies 109. Each contact roller assembly 109 includes a crectangular plate 110 having vfour spaced apertures therethrough, through each of ,which extends a pin 111 supporting a pair of contact .rollers 112. Suitable springs may be provided, encircling the pins 1-11,-to bias the contact rollers 112 toward eachother, and into-engagement with both the movable guide rail 108 and the stationary guide rails 110. This construction is set out cylinder casing 119 containing asuitable'fluid, such as oil 120. The cylinder casing 119 has a closure ,cap 121 atone end, with which .theapertured lug 94may -be integrally formed. At the other ;end of the cylinder casing 119 is an aperturedclosure cap 122 having acenpressure P across the orifice opening 36 to quickly bring about are extinction. If, however, the piston 49 remains constantly stationary at all times, the isolating gap distance between the contacts '37, 38, in the open position of :the interrupter, might be hazardous, and, therefore, it is proposed to subsequently effect the isolating travel of the piston 49 together with the operating cylinder 31.

tral opening 123, through which the piston rod 92 ;ex-

tends. A suitable gasketed seal 124 may be provided 210 prevent interexchange between the .oil and SP fluids.

Stationarily mounted between the outer cylinder casing 119 and the inner operatingcylinder 118 is an apertured ring 125, having openings 126 therethrough, which are controlled -by ball valves 127. The ball valves 2127 readily permit the passage of fluid :from right to left through openings 1216, .as viewed in *Fig. 6, but the ball valves 127,0ppose the rightward passage of fluid through the openings 126, as will .be obvious.

The region to the leftof ring ,125 is entirely filled with oil, whereas the region to the right \of ring has an oil level at 121a with .air .above ,it to accommodate the volume of piston rod'92, which ;moves within shockabsirber assembly 93 during :the working part of the stro e. During the opening operation, the .cperating cylinder 106 (Fig. 5B) moves upward, carrying the movable contact ,33 away from the relative y stationary contact 37 and compressing the fluid, such as SP gas, Within the region 128 below piston 91. This gas will be forced out through theorifice opening 129, provided byorifice member 130, in a manner similar to that heretofore described. The upward movement of the operatingcylinder 106 will be guided by the guide rails 10:1, 108 and the roller assemblies 109. This will reduce friction,,and will readily transfer current between the movable contact,38,,rnovable guide rails 108 and the stationary guide rails 101, which are connected to the terminal stud 99.

The piston '91 is initially stationary, since the leftward movement of the piston rod 92, as vieweddn Fig. 6, will be opposed by the oil pressure built up n chamber 131. In other words, the piston 113 is attempted to be moved into chamber 131, and there is no place for the oil to move, the valves 127 closing the openings 126, and the spring 115 closing the opening 117. However, when the surface 132a (Fig. B) of the spider plate 132 strikes the piston 91, and increases the leftwardpressure exerted upon the piston rod 92, as viewed in Fig; 6, the oil pressure within the region 131 will be suflicient to compress the spring 115 and permit the oil to pass out of sembly 93 provides a variable resistance means to rapid movement of the piston 91. Initially, there isa high resistance to rapid movement of the piston 91, and subsequently relatively free retraction of the piston 91 with the operating cylinder 106 is permitted.

From the foregoing description, it will be apparent that there is provided an improved operating cylinder arrangement, in which the piston therein is initially '1. A fluid-blast circuit interrupter including contact means for establishing an arc, a movable operating cylinder, a piston disposed within said operating cylmder, an operating mechanism for effecting contact separation andfor driving said movable operating cylinder to the openposition over the piston for fluid compression therebetween, means for directing the compressed fluid against the are, a two-stageshock absorber connected to sa1d piston for providing two types of loading therefor for the retraction thereof, said two-stage shock absorber isolating gap distance between the separated contacts,

stationary, and subsequently moves with the movable across the orifice openings. The shock-absorber assem blies 51, 93 have the characteristics of oifering high resistance over a short portion of the piston stroke, and then a minimum resistance for the remainder of the travel, in which the piston is retracted to the full-open position of the contacts by the operating cylinder.

It will be noted that both shock absorbers 51, 93

' are of the two-stage type, the resistance or loading they offer to retraction of the respective fixed pistons 49, 91, beinga function of the position of the fixed pistons 49, 91. During thefirst stage of operation of the shock absorbers 51, 93, during initial retraction of the pistons 49, 91 high resistance or loading is encountered. During the second stage, following said initial retraction of the pistons 49, 91, low resistance or loading is afforded by the shock absorbers 51, 93.

The resistance device 51, 93, as disclosed further eliminates the necessity of external shock absorbers, and, with a large oil reservoir associated with the device 51, 93, the interrupter may be mounted in any position, either horizontal or vertical. During the closing of the interrupter, the secondary pistons 49, 91, may be retrieved to their initial closed-circuit position by the retrieving springs 89 or 140.

An application of the principles of the present invention'to fluid-blast interrupters utilizing operating cylinder arrangements results in very rapid build-up of pressure across the orifice, and a consequent high-velocity injection of fluid through the orifice and into engagement with the established arc. By the feature of the piston being movable during the latter part of the opening stroke, an adequate isolating gap distance is provided between the separated contacts so that no flashover may occur therebetween in the fullyopen-circuit position of the interrupter.

Although there have been shown and described specific operating cylinder arrangements, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may the second stage of loading aflorded by the two-stage shock absorober coming into existence after a predetermined initial retracting distance covered by said piston toward the end of the opening operation and following are extinction, and the two-stage shock absorber having the characteristics during the second stage of loading of affording only slight resistance to the operating mechanism during isolating retraction of said piston with said operating cylinder at the end of the opening operation of the interrupter.

. 2. The combination in a fluid-blast circuit interrupter of a relatively stationary contact, a movable operating cylinder, a movable contact movable with said operating cylinder and separable from said relatively stationary contact to establish an arc, a piston disposed within said operating cylinder, an operating mechanism for effecting contact separation and for driving said movable operating cylinder to the open positionover the piston for fluid compression therebetween, means for directing the compressed fluid against the arc, a two-stage shock absorber connected to said piston for providing two types of loading therefor for the retraction thereof, said two-stage shock absorber having the characteristics during the first stage of loading of affording relatively high resistance to the operating mechanism during initial retracting movement of said piston during the opening operation from the closed-circuit position thereof, said operating mechanism moving said operating cylinder into abutting engagement with said piston toward the end of the opening operation for carrying said piston therewith for obtaining an appreciable isolating gap distance between the separated contacts, the second stage of loading aflorded by the twostage shock absorber coming into existence after'a predetermined initial retracting distance covered by said piston toward the end of the opening operation and following arc extinction, and the two-stage shock absorber having the characteristics during the second stage of loading of affording only slight resistance to the operating mechanism during isolating retraction of said piston with said operating cylinder at the end of the opening operation of the interrupter.

3. The combination in a fluid-blast circuit interrupter of a relatively stationary contact, means defining an orifice, a movable operating cylinder carrying said orifice, a movable contact movable with said operating cylinder and separable from said relatively stationary contact "to draw an are through said orifice, a piston disposed within said operating cylinder, an operating mechanism for eifecting contact separation and for driving said movable operating cylinder to the open position over the piston for fluid compression therebetween, means including said orifice for directing the compressed fluid against the arc, a two-stage shock absorber connected to said piston for aeaeyoro providing two types o'floading therefor for the retraction said two-stage -shoek-absorber having the charjduring the fi-rst-stage of loading of affording rlatively high resistance-to-the operating mechanism during initial retracting movement of said piston during theopening operation from the closed-circuit position thereof, said operating mechanism moving said operating cylinder into abutting engagement with said piston toward the end of the opening operation for carrying said piston therewith for obtaining an appreciable isolating gap distance between the separated contacts, the second stage of loading afforded by the two-stage shock absorber coming into existence after a predetermined initial retracting distance covered by said piston toward the end of the opening operation and following arc extinction, and the two-stage shock absorber having the characteristics during the second stage of loading of affording only slight resistance to the operating mechanism during isolating retraction of said piston with said operating cylinder at the end of the opening operation of the interrupter.

4. A circuit interrupter including a hollow insulating casing, means supporting a relatively stationary contact adjacent one end of said hollow insulating casing, a terminal bushing extending into the other end of said hollow casing, a movable operating cylinder, the interior end of said terminal bushing supporting said movable operating cylinder, a movable contact cooperable with said relatively stationary contact to establish an arc, the movable operating cylinder carrying said movable contact, a piston disposed within said operating cylinder, an operating mechanism for effecting contact separation and for driving said movable operating cylinder to the open position over the piston for fluid compression therebetween, means for directing the compressed fluid against the arc, a two-stage shock absorber connected to said piston for providing two types of loading therefor for the retraction thereof, said two-stage shock absorber having the characteristics during the first stage of loading of affording relatively high resistance to the operating mechanism during initial retracting movement of said piston during the opening operation from the closed circuit position thereof, said operating mechanism moving said operating cylinder into abutting engagement with said piston toward the end of the opening operation for carrying said piston therewith for obtaining an appreciable isolating gap distance between the separated contacts, the second stage of loading afiorded by the two-stage shock absorber coming into existence after a predetermined initial retracting distance covered by said piston toward the end of the opening operation and following arc extinction, and the two-stage shock absorber having the characteristics during the second stage of loading of aflording only slight resistance to the operating mechanism during isolating retraction of said piston with said operating cylinder at the end of the opening operation of the interrupter.

5. A circuit interrupter including a hollow insulating casing, means supporting a relatively stationary contact adjacent one end of said hollow insulating casing, a terminal bushing extending into the other end of said hollow casing, an orifice member, a movable contact, an operating cylinder mounted on the inner end of said terminal bushing and carrying said orifice member and said movable contact, the movable contact being separable from said relatively stationary contact to establish an are through said orifice member, a piston disposed within said operating cylinder, an operating mechanism including an insulating operating rod extending longitudinally of said terminal bushing for effecting movement of said operating cylinder over said piston and also contact separation, a two-stage shock absorber connected to said piston for providing two types of loading therefor for the retraction thereof, said two-stage shock absorber having during the opening operation Tfrom the closed-circuit .posigtionthereof, said operating mechanism moving saidoperating cylinder into abutting engagement with said piston toward the end of the opening operation for carrying said piston therewith for obtaining an appreciable isolating gap distance between the separated contacts, the second stage of loading afforded by the two-stage shock absorber coming into existence after a predetermined initial retracting distance covered by said piston toward the end of the opening operation and following are extinction, and the two-stage shock absorber having the characteristics during the second stage of loading of affording only slight resistance to the operating mechanism during isolating retraction of said piston with said operating cylinder at the end of the opening operation of the interrupter.

6. The combination in a fluid-blast circuit interrupter of a movable operating cylinder carrying a movable contact, a relatively stationary contact cooperable with said movable contact to establish an are, a relatively fixed piston over which said movable operating cylinder moves to compress fluid, an operating mechanism for driving said operating cylinder over said fixed piston, orifice means associated with said movable operating cylinder and movable contact to direct said compressed fluid toward the established arc, a two-stage shock absorber connected to said piston for controlling the motion of said relatively fixed piston and operable during the first stage to initially oppose any rapid movement of said relatively fixed piston so that compression of fluid may readily take place, said two-stage shock absorber being operable during the second stage during the latter portion of the circuit interrupter opening operation and following a predetermined retracting motion of the piston to permit relatively free further retraction of said relatively fixed piston an appreciable isolating distance travel with said operating cylinder and movable contact for insuring an adequate isolating distance between the contacts in the fully open circuit position thereof, and said two-stage shock absorber imposing only a light load upon said operating mechanism during the second stage of the operation thereof.

7. The combination in a fluid-blast circuit interrupter of a movable operating cylinder, a movable contact movable with said movable operating cylinder at least during a portion of the opening travel of said movable operating cylinder, at relatively stationary contact cooperable with said movable contact to establish an arc, a relatively fixed piston over which said movable operating cylinder moves to compress fluid, an operating mechanism for driving said operating cylinder over said fixed piston, orifice means associated with said movable operating cylinder and movable contact to direct said compressed fluid toward the established are, a two-stage shock absorber connected to said piston for controlling the motion of said relatively fixed piston and operable during the first stage to initially oppose any rapid movement of said relatively fixed piston so that compression of fluid may readily take place, said two-stage shock absorber being operable during the second stage during the latter portion of the circuit interrupter opening operation and following a predetermined retracting motion of the piston to permit relatively free further retraction of said relatively fixed piston an appreciable isolating distance travel with said operating cylinder and movable contact for insuring an adequate isolating distance between the contacts in the fully open circuit position thereof, and said two-stage shock absorber imposing only a light load upon said operating mechanism during the second stage of the operation thereof.

(References on following page) 1 1 References Cited in the file of this patent Y UNITED STATES PATENTS 528,791 1,768,949 Denison 1 July 1, 1930 828,466 r 2,219,171 B-alachowsky oct. 22, 1940 671,502 2,429,311 Gay Oct; 21, 1947 -12 FOREIGN PATENTS France Aug. 25, 1921 France Feb. 14, 1 938 Germany Feb. 8, 1939 

